Hi Yuhas,
Excuse me for the fat finger typo.
The offending line should read.
If you are giving the bare minimum amount of light for the plants to grow when you start up your planted tank, when the bulb ages and diminishes in brightness over time then your plants will stop growing.
So if you are already giving ample light, some drop in the bulb brightness will still be ok.
Hope that clarifies matters.
Sorry for the manglish!
Regards
Stan